302 NORMAL HISTOLOGY. 



sections are compressed into tiny folds or ridges, the paraffin is too 

 soft and the block must be somewhat chilled. 



Before paraffin-sections can be stained it is necessary to remove 

 the paraffin. If the tissues are sufficiently coherent, this can be 

 done by dropping the sections into xylol or chloroform ; but if this 

 would cause a disintegration of the sections, they must be affixed to 

 slides or cover-glasses by means of a cement which shall hold the dif- 

 ferent parts of the tissues in their proper relative positions after the 

 paraffin has been removed. The simplest cement for this purpose 

 is Mayer's albumin mixture, prepared as follows : beat up the white 

 of an egg and allow the froth to liquefy. Then add an equal bulk 

 of glycerin and a few pieces of camphor (for the preservation of 

 the mixture). This cement is applied to the clean surface of a 

 slide, or cover-glass in a very thin layer with the side of a camel's- 

 hair brush, care being taken to leave no air-bubbles. The paraffin- 

 sections are removed from the knife with a fine camel's-hair 

 brush or a small, but rather stiff feather inserted into a handle, 

 and placed upon the coating of cement. They are then flat- 

 tened out with the brush or feather and pressed against the glass to 

 remove superfluous cement. If the sections have rolled, unrolling will 

 be facilitated by Avarming the sections with the breath. The cover- 

 glasses are set aside to dry a little, and are then heated to render 

 the albumin insoluble. This requires some practice. The manipu- 

 lation is intended to accomplish the following results : the paraffin 

 melts at a lower temperature than that at which the albumin is 

 coagulated, and this fact is utilized to remove all excess of the 

 cement, which is washed away from the tissues by the flow of melted 

 paraffin. The residual albumin is sufficient to make the section 

 adhere to the glass when subjected to a high enough temperature to 

 cause its coagulation. The albumin should be dried to a consider- 

 able extent before it is converted by the heat into its insoluble form, 

 otherwise it will coagulate in opaque masses. To bring about the 

 desired results the cover-glass, held in a pair of forceps, is waved 

 over a flame until the paraffin is seen to melt. That tempera- 

 ture is maintained for a few moments, and then the cover-glass 

 is heated until vapors are distinctly seen to rise from its surface. 

 Great care must be taken not to scorch the sections. When the 

 sections have been cemented to them the cover-glasses are placed in 

 absolute alcohol to dehydrate them, and are then treated with xylol, 

 chloroform, or some other solvent of paraffin. The solvent is then 



